The present invention relates to a power steering apparatus for performing power steering through a motor.
A hydraulic power steering apparatus has been conventionally used to steer wheels with a small steering force. In this case, oil leakage must be strictly prevented, and such a power steering apparatus cannot be made compact. In addition, a hydraulic pump and pipes must be used, resulting in high cost. In order to eliminate these drawbacks, a rotational force of a motor can be directly utilized as an auxiliary force.
In a conventional electronic power steering apparatus, a rotor of the motor must be rotated in the reverse direction by the number of times required for turning when straight driving is resumed after turning. A motor speed during reverse rotation is obtained by a self-aligning torque generated by wheel drag. In this case, a frictional force occurs between a brush or the like in the motor and acts against rotation of the rotor. The rotor cannot thus be sufficiently rotated only by the self-aligning torque. This phenomenon typically occurs when a magnetic motor is used. The insufficiency must be compensated by providing an additional torque to the steering wheel. As a result, the driver experiences abnormal steering.